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Incomplete Dominance
When neither allele is completely dominant over the other.
Ex. Red RR x White rr = 1/2 Pink Rr
Codominance
When both alleles are fully expressed and both create an effective product- like blood types, specifically blood type AB.
Ex. Red fish and blue fish make a red and blue fish
Epistatsis
When the product of one gene may modify the phenotypic expression of the other. A good example of this is albinism- you need to make the pigment and then make the pigment color; however if you don't make the pigment in the first place the pigment color doesn't matter.
Ex. The rats are albino because they didn't make Cc or CC, which is the pigment- they made cc instead
Continuous Variation and Polygenic Theory of Inheritance
When some traits have multiple genes that act together to determine the phenotype. Since there is such a large range of variation, we see a gradation in the in the degree of difference- which makes a bell-shaped curve on a graph.
Ex. Height & weight
Pleiotropy
When an allele has more than one effect on a phenotype, like white cats having blue/green eyes, yellow mice, and dwarfism.
Ex. In dwarfs, dd = no dwarfism, Dd = dwarfism due to underdeveloped limbs but developed torso, DD = lethal due to there being not enough bone for the baby to survive.
Human Female Chromosome
XX
Human Male Chromosome
XY
Sex Linkage
Since the Y chromosome carries very few traits, most are passed on to X; this makes it so it shows up easier in males than females, as females have a backup X while males do not. (It can still show in females though). The X chromosome with the sex-linked trait MUST come from the mother.
Ex. Color blindness, Hemophilia, ALD, Muscular Dystrophy, albinism in fruit fly eyes.
Thomas Morgan
The guy who came up with the Chromosomal Theory of Inheritance- figured out alleles on chromosome were a thing and studied fruit flies. He determined that different genes could be on the same chromosome and inherited together as well- like they were linked.
The Chromosomal Theory of Inheritance
Genes occupy specific positions on the chromosome, and chromosomes undergo the process of segregation and independent assortment in meiosis.
Important thing to know with sex linkage:
Make sure to split your end phenotypic and genotypic ratio based on Gender!!!
Autosomal Recessive Disorders
When there is an increased possibility of passing on recessive traits if close relatives mate. This is known as inbreeding, and is seen in zoo animals and unethical puppy mills.
Cystic Fibrosis (CF)
When the sodium/potassium pumps malfunction, which causes high extracellular chloride concentration and causes mucus to be thicker and stickier than usual. The mucus builds up in important organs and glands, and causes eventual death. It is an example of pleiotropy.
Autosomal Recessive
Sickle Cell Anemia
Red blood cells can become sickle-shaped instead of round/concave, and when oxygen is low they can come together and clog blood vessels. This can cause weakness, pain, organ damage, paralysis and more. If heterozygote carriers have some symptoms, then they are incomplete dominant- they also have an advantage against malaria.
Ex. normal blood cell AA, sickle cell aa, Aa some sickle cells.
Autosomal Recessive
Phenlyketonuria (PKU)
When the liver cannot break down the amino acid phenylalanine so it accumulates in the blood. Causes mousy odor, broad shoulders, missing skin pigment, difficultly walking, and mental retardation. Easily manageable if phenylalanine is not consumed.
Autosomal Recessive
Albinism
The lack of pigment in skin and hair, an example of epistasis.
Autosomal Recessive
Tay Sachs
When lysosomes cannot break down lipids so they accumulate in the brain cells. Babies become blind by age 1 and are usually dead by age 5.
Autosomal Recessive
Autosomal Dominant Disorders
Appear by mutation originally, if they are immediately lethal then the gene is not passed on. If not lethal, then the gene will appear in offspring in a homozygous or heterozygous situation.
Achondroplasia
The allele codes for shortened bone growth, and results in dwarfism where the torso is normal but the arms and legs are smaller. Normal-sized individuals are homozygous recessive, dwarfs are heterozygous, and homozygous dominant individuals do not make enough bone to survive (dominant lethal allele.)
Autosomal Dominant
Huntington's Disease
An irreversible degenerative disease of the brain and nervous system that is fatal. It is very rare, but is passed on because symptoms do not appear until the afflicted person has already had children. We can test for it, as we worked on finding it as it was deadly and hard to identify.
Autosomal Dominant
Polydactyly
Extra fingers and toes; most extra fingers are on the pinky side but some can be on the thumb or in the middle.
Autosomal Dominant
Sex-Linked Recessive Disorders
Inherited on the X chromosome; since males only need one of these alleles to show the trait they are more common in males than females.
Red-Green Color Blindness
The cones in the eyes are unable to distinguish between red and green pigments. A normal person can see 150 colors, a colorblind person can see 25 or less.
Sex-Linked Recessive
Hemophilia
A blood plasma disorder where clotting factors are missing or non-functioning, causing excessive bleeding.
Sex-Linked Recessive
Duchenne Muscular Dystrophy
An allele for a muscle protein that is missing or non-functioning, causing progressive weakening and loss of muscle.
Sex-Linked Recessive
Multifactorial Disorders
These are the many disorders that are polygenic or have a multifactorial basis; they usually have a genetic and environmental component.
Ex. Heart disease, cancer, alcoholism, weight, height
Pedigree
A diagram that shows the occurrence of a genetic trait in several generations of a family, since you can't do human breeding.
